1. Field of the Invention
The present invention relates generally to wire bonding of semiconductor devices, and more particularly, to a method of bonding a wire and a wire bond structure formed by the same.
2. Description of the Related Art
In recent years, as portable electronic devices have been scaled down (e.g., smaller, thinner and lightweight) where semiconductor devices are used. As such, the process for packaging semiconductor devices has also been scaled down. In these semiconductor devices, a conventional packaging process may include only one semiconductor chip, a multi-chip package (MCP) in which a plurality of semiconductor devices are arranged or stacked has been developed and widely used. An MCP may be used, for example, in electronic devices and telecommunication devices.
In an MCP, the arranged or stacked semiconductor chips may perform different functions for various operations. Alternatively, the arranged or stacked semiconductor chips may perform the same function to increase the charge potential thereof. Because the MCP includes at least two or more arranged or stacked chips, there many be restrictionin manufacturing the semiconductor devices.
For example, one problem associated with an MCP may be the diameters of wires used for wire bonding. That is, as the length of a wire increases, the diameter of the wire should also increase so as to prevent the bending or sweeping of the wire. Thus, because an MCP includes various chips that are different in size mounted therein, a smaller semiconductor chip may have a longer wire bonding than a larger semiconductor chip. In this case, the longer wire may undesirably bend which may come into contact with an adjacent wire of another chip.
Further, another problem associated with an MCP may be that a wire may be swept (e.g., wire being out of position or even losing contact to the chip pads due to the flow of epoxy molding compound (EMC) caused by an injection of the EMC during the molding process of the packaging processes).
Accordingly, as semiconductor devices become more highly integrated, chip pads required for wire bonding of the semiconductor devices may be scaled down. For this reason, wires that are large in diameter may not be used.
FIGS. 1 through 4 are cross-sectional views illustrating a conventional process of bonding a wire to a chip pad.
Referring to FIG. 1, a conventional wire bonding of semiconductor chips may generally utilize a ball bonding process. For example, as shown in FIG. 1, a ball-shaped prominence 15 may be formed at a terminal portion of a wire 10 which may have a diameter of D1 by using a capillary of a wire bonding machine. As shown in FIG. 2, the prominence 15 may be attached to a conductive pad 20 which has a width of D4.
During the attaching process, the prominence 15 is pressed against the conductive pad 20, which may deform into a prominence 15′ The prominence may then be bonded to the conductive pad 20. Thereafter, as the capillary moves and continues to provide a conductive material, the wire 10 may extend from the prominence 15′. The extended wire 10 may be bonded by a stitch bonding method to another pad, for example, an electrode pad that may be disposed on a carrier on which a semiconductor chip may be mounted.
However, to form a bond in a ball bonding manner, (i.e., when the ball-shaped prominence 15′ is bonded to the pad 20), the width D3 of the prominence 15′ should not be greater than the width D4 of the pad 20. In other words, the width D4 of the pad 20 should be greater than the width D3 of the prominence 15′ which may be bonded to the pad 20.
The width D3 of the bonded prominence 15′ may depend on the width D2 of the initial ball-shaped prominence 15 of FIG. 1. The width D2 of the ball-shaped prominence 15 depends on the diameter D1 of the wire 10 that is provided to the capillary, which may be formed of, for example, gold. As a consequence, the diameter D1 of the wire 10 depend on the width D4 of the pad 20. That is, the width D4 of the pad 20 may place a limit on the diameter D1 of a usable wire 10.
Accordingly, as shown in FIG. 3, if a conductive pad 21 formed on a semiconductor chip 30 is scaled down, the diameter D11 of wire 11, which may be bonded to the pad 21, may be limited by the width D41 of the pad 21 since the width D31 of a bonded prominence 16 may be limited by the width D41 of the pad 21. That is, only a wire 11 of a smaller diameter than the value D11 may be used in the wire bonding process. However, if the bonding wire 11 becomes longer, then wire 11 may be undesirably bent or swept.
For example, referring to FIG. 4 which illustrates an MCP, a first semiconductor chip 31 may be mounted on a carrier 40 during a packaging process of semiconductor devices, and a second semiconductor chip 35 may be mounted on the first semiconductor chip 31. With the higher integration of semiconductor devices and reduction of design rules, a small pitch first pad 21 and a small pitch second pad 25 may be mounted in the first and second semiconductor chips 31, 35, respectively. In order to electrically connect the first and second pads 21, 25 to a first electrode pad 51 and a second electrode pad 55, respectively, a first wire 13 and a second wire 17, respectively, may be mounted using a wire bonding process. The first and second electrode pads 51, 55 may be formed on the carrier 40.
Here, the diameters of the first and second wires 13, 17 are limited by the sizes of the first and second pads 21, 25, respectively. As a result, this may require the first and second wires 13, 17 to berelatively small. Further, the second wire 17, which may have a longer length L2 than the length L1 of the first wire 13, may bend due to the lack of tension in the second wire 17 or the second wire 17 may be swept by the flow of epoxy molding compound (EMC) caused by an injection of the EMC during the molding process. Additionally, even the first wire 13 having the relatively smaller length L1 may be bent or swept because the first pad 21 and second pad 25 are very thin.
However, even if wires 13, 17 may be bent or swept, the wires 13, 17 maynot be provided with a sufficient diameter because the prominence 16 that depends on the fine sizes of the first and second pads 21, 25 may provide a limited size.